Field of the Invention
The present invention relates to a toner for developing electrostatic images (electrostatic latent images) used in image-forming methods in the manner of electrophotography and electrostatic printing.
Description of the Related Art
Due to the development of computers and multimedia in recent years, there is a desire for a means of outputting high-definition full-color images in a wide range of fields from the office to the home.
In addition, there is a demand for high durability without decreasing quality even when copying or printing large numbers of prints during use in offices where copying or printing is carried out frequently. On the other hand, in the case of use in small offices or at home, image-forming apparatuses are being required to be more compact in addition to allowing the obtaining of high-quality images from the viewpoints of saving on space, saving on energy and reducing weight. In order to response to these demands, there is a need to further improve toner performance in terms of environmental stability, resistance to contamination of members, low-temperature fixability, development durability and storage stability.
In the case of full-color images in particular, images are formed by superimposing color toners, and color reproducibility decreases and uneven coloring ends up occurring unless each color of toner is developed in the same way. The effect on development becomes large as a result of the pigment or dye used as toner colorant precipitating on the surface of the toner particles.
Moreover, fixing performance and color mixability during fixation are important when forming full-color images. Although a binder resin suitable for low-temperature fixability is selected in order to achieve a desired increase in speed, the effects of this binder resin on developability and durability are also considerable.
One example of a factor responsible for fluctuations in toner storage stability or amount of electric charge caused by temperature and humidity is the occurrence of a phenomenon in which toner release agent and resin components exude from inside toner particles onto the surface (to also be referred to as bleeding), and this bleeding causes a change in the surface properties of toner particles.
A method consisting of covering the surface of toner particles with resin is one method for solving such problems.
Japanese Patent Application Laid-open No. 2006-146056 discloses a toner that strongly adheres inorganic fine particles to the surface thereof as a toner that demonstrates superior high-temperature storability as well as printing durability in normal temperature, normal humidity environments and high temperature, high humidity environments during image output.
However, even though inorganic fine particles are strongly adhered to the toner particles, there is a need for further improvement with respect to durability and contamination of members in harsh environments due to the occurrence of bleeding caused by the release agent and resin composition from the gaps between inorganic fine particles, and the release of inorganic fine particles due to deterioration of with time.
In addition, Japanese Patent Application Laid-open No. H03-089361 discloses a method for producing a polymerized toner obtained by adding a silane coupling agent to the reaction system in order to obtain a toner having a narrow charge distribution and little charge humidity-dependency without exposing colorant or polar substances on the surface of the toner particles.
However, in this method, since the amount of silane compound that precipitates on the surface of the toner particles and hydrolysis and condensation polymerization of the silane compound are inadequate, further improvement is required with respect to environmental stability and development durability.
Moreover, Japanese Patent Application Laid-open No. H09-179341 discloses a method for using a polymerized toner containing a silicon compound provided in the form of a continuous thin film on a surface portion as a method for controlling the amount of toner charge and forming high-quality output images without being influenced by temperature or humidity.
However, due to the large polarity of the organic functional groups, the amount of silane compound that precipitates on the surface of the toner particles and hydrolysis and condensation polymerization of the silane compound are inadequate, the degree of crosslinking is weak, and further improvement is required with respect to changes in image density caused by changes in charging performance at high temperature and high humidity as well as contamination of members caused by deterioration with time.
Moreover, Japanese Patent Application Laid-open No. 2001-75304 discloses a polymerized toner having a coated layer formed by mutually adhering blocks of particles containing a silicon compound as a toner for improving flowability, release of fluidizing agent, low-temperature fixability and blocking.
However, bleeding attributable to release agent and resin components from gaps between clumps of particles containing silicon compounds occurred easily. In addition, the amount of silane compound precipitating on the surface of the toner particles and hydrolysis and condensation polymerization of the silane compound were inadequate, thereby requiring further improvement with respect to changes in image density caused by changes in charging performance at high temperature and high humidity as well as contamination of members caused by melt adhesion of toner.
On the other hand, the use of a crystalline resin for the binder resin has been proposed as a means of realizing low-temperature fixability while satisfying storage stability.
For example, Japanese Patent No. 5084482 discloses a means of realizing both low-temperature fixability and long-term storability by combining the use of crystalline polyester and amorphous polyester containing an aliphatic alkyl segment for use as a binder resin.
However, it was still necessary to slightly improve long-term storability in order to achieve additional low-temperature fixability.